Such a filter is known from WO 99/30799. In this previously known filter, the element head forms the complete inlet elbow. It is immediately adjacent to the inlet. Accordingly, the housing head portion does not contribute to form the inlet elbow. The first sealing surface configured within the housing head portion is virtually perpendicular to the element axis, the same applies to the second sealing surface. The second sealing surface is formed by a sealing ring that acts in the axial direction. It cannot be ruled out that said ring is subjected to such a load during insertion that it slips out of its holding device. A mechanical guide is further necessary, said guide causing the second sealing surface to fit precisely relative to the first sealing surface and concurrently these two sealing surfaces to be pressed together during insertion.
Another disadvantage of the previously known filter is that a differential pressure measurement between inlet and outlet is difficult. In the document mentioned, the inlet elbow has a special connecting sleeve for detecting the pressure inside the inlet elbow. This makes the mechanical implementation complicated and the additional sealing requires special provisions.
The element head with its inlet elbow is also difficult to manufacture. Natural methods for removing the mould cannot be used here. Furthermore, the filter element becomes more bulky on account of the relatively large element head. As is known, the filter element is intended to wear and be replaced after a certain number of hours operation.